class MyTest{
    public static int count=0;
    public static void add(){
        synchronized(MyTest.class) {
            count++;
        }
    }
}
public class Test4 {
    public static void main(String[] args) throws InterruptedException {
        MyTest t = new MyTest();
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 50000; i++) {
                t.add();
            }
        });
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 50000; i++) {
                t.add();
            }
        });
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println("count=" + t.count);
    }
}